This research program investigates questions concerning immune responses elicited by viral and plasmid vectors. Results are relevant both to vaccine potency and mechanisms of action, and also to effects of immune responses on the use of viral and plasmid vectors for gene therapy, either blocking therapy or causing immunopathology. Our work focuses on the mouse influenza system. Main projects: a) Heterosubtypic immunity (het): Protection against influenza A virus challenge is induced in animals by prior infection with a virus subtype differing from the challenge virus. This also provides a model for sequential exposures to related viral vectors. We have shown that neither CD4+ nor CD8+ T cells are required at the time of challenge, and that passive antibody does not transfer het. Mice lacking MHC class I display het, and in this case CD4+ cells are required for optimal protection. Role of secretory pathway in het: Mice with a targeted disruption of the gene for J chain have been studied for their ability to mount protective responses against heterosubtypic influenza infection. The secretory pathway was not required for such immunity. Mice with other antibody defects are under study. b) Immune responses induced by plasmid DNA: Plasmid DNA is under study as a vaccine and also as a gene therapy vector; such products are in clinical trials. We are studying effects of plasmids encoding influenza virus antigens. Potency and specificity of immunity have not been adequately examined in previous studies, and we are performing validation studies in this area, as well as studies of protective mechansisms. c) Effect of transcription factor deficiencies on antibody responses to influenza virus. Knockout mouse strain deficient in certain DNA binding proteins have been produced by collaborators. We are studying ability of these mice to produce antibody of various isotypes in response to influenza virus infection.